Additive blend for enhancing water vapor permeability and increasing cell size in thermoplastic foams

ABSTRACT

Polymeric foam and polymeric foam products that contain a foamable polymer material, at least one blowing agent, an additive blend of polyethylene oxide and a copolymer of polystyrene and maleic anhydride, and optionally, an infrared attenuating agent, are provided. In exemplary embodiments, the polyethylene oxide is ethoxylated polyethylene oxide. Additionally, in at least one embodiment, the blowing agent includes at least one hydrofluorocarbon blowing agent. The blend of ethoxylated polyethylene oxide and copolymer of polystyrene and maleic anhydride provides a water vapor permeability of 1.1 perm inch or greater in the extruded foam product and increases the average cell size of the foam product without detrimentally affecting physical or thermal properties of the product. Additionally, the additive acts as a cell enlarger, a water vapor permeability enhancer, a plasticizer, and a processing aid. A method of forming an extruded foam product is also provided.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

The present invention relates generally to extruded foam products, andmore particularly, to a polystyrene foam containing a blend ofethoxylated polyethylene oxide and a styrene/maleic anhydride copolymerwhere the polymer foams have an improved water vapor permeability, havean enlarged average cell size, and possess no ozone depleting potentialand a low global warming potential. A method of forming such polymerfoams is also provided.

BACKGROUND OF THE INVENTION

Foamed resinous structures are useful in a wide variety of applicationssuch as thermal insulation, in cushions, as packaging, and asadsorbents. Extruded foams are generally made by melting a polymertogether with any desired additives to create a polymer melt. A blowingagent is mixed with the polymer melt at an appropriate temperature andpressure to produce a foamable gel mixture. The foamable gel mixture isthen cooled and extruded into a zone of reduced pressure, which resultsin a foaming of the gel and the formation of the desired extruded foamproduct. As will be appreciated, the relative quantities of thepolymer(s), blowing agent(s), and additives, as well as the temperatureand manner in which the pressure is reduced will tend to affect thequalities and properties of the resulting foam product.

Traditional blowing agents used for extruded foam products includechlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). One ofthe advantages of both CFC and HCFC blowing agents is their highsolubility in a polymer melt during the manufacturing process. Higherblowing agent solubility promotes a reduction in viscosity when theblowing agent is mixed with the polymer melt. In turn, lower viscosityleads to lower energy requirements for mixing. On the other hand, amajor disadvantage to these traditional blowing agents is that anincreasing number of governments worldwide have mandated the eliminationof CFC and HCFC blowing agents due to growing environmental concerns.CFCs, and many other halocarbons, have come to be recognized as seriousglobal environmental threats due to their ability to cause stratosphericozone depletion and global warming. The ozone depletion and globalwarming impact of chemicals such as CFCs and HCFCs are measured by theozone depletion potential (ODP) and global warming potential (GWP)respectively.

In view of the mandatory phase out of blowing agents with a high ODP anda high GWP, there has been a movement to replace the conventionalblowing agents with more environmentally friendly blowing agents, suchas hydrofluorocarbons (HFCs) and CO₂, in insulating foam applications.Although HCFCs provide a superior thermal barrier compared to HFC andCO₂, the chlorine present in the HCFCs possesses an ozone depletionpotential. Additionally, over time, the chlorofluorocarbon gas phaseremaining in the foam is released into the atmosphere, thereby reducingthe insulative value of the foam and potentially further contributing toozone depletion and to the global warming potential. In addition, eachof the “non-conventional” blowing agents leads to a different cell sizeand morphology, depending on the particular blowing agent chosen.Additionally, the cell sizes of the foams produced by these generallyenvironmentally friendly blowing agents are too small to provide anacceptable insulative value to the foamed product and generally resultsin a higher density and a more costly product.

In addition, the water vapor permeability of the foams produced withHCFCs typically have a water vapor permeability of 1.0 perm inch orless. Desirably, the water vapor permeability of extruded foam boards isgreater than 1.0 perm inch. Improving the water vapor permeability inextruded foam boards is becoming an important factor in buildingconstruction design and applications. The water vapor permeability ofextruded foam boards is an important factor in inhibiting the potentialfor condensation as well as mold and fungal growth on the foamed boardsand in the wall system in which the foam boards are used. When water,dust, and other microbial nutrients contaminate the foam board, theyprovide a support medium for the growth of bacteria, fungi, and/or moldin and on the foamed board. Bacterial, fungal, and mold growth may causeodor, discoloration, and/or product deterioration. Previous attempts toeliminate mold growth have been focused on limiting the intrusion ofliquid water and the condensation of water vapor within the wallassembly.

Despite previous attempts to reduce the ODP and GWP, there remains aneed in the art to achieve an extruded polymer foam that has an improvedwater vapor permeability and an increased cell size when non-HCFCblowing agents are used, that maintains the positive physical propertiesof conventional extruded polystyrene foams, that provides a foam productwith increased insulation value (R-value), and that meets the stringentrequirements for a reduction in the global warming potential and ozonedepletion potential.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a composition forforming a closed cell, rigid thermoplastic polymer foam that includes afoamable polymer material, at least one blowing agent, an additive blendof polyethylene oxide and a styrene/maleic anhydride copolymer, andoptionally, an infrared attenuating agent. The blowing agent may beselected from hydrofluorocarbons, C₁ to C₉ aliphatic hydrocarbons, C₁ toC₃ aliphatic alcohols, carbon dioxide, acetone, natural gases, air,water, ketones, ethers, methyl formate, hydrogen peroxide, andcombinations thereof. The blend of polyethylene oxide and astyrene/maleic anhydride copolymer provides a water vapor permeabilityof 1.1 perm inch or greater to foamed products made utilizing theinventive composition. In exemplary embodiments, the foamable polymermaterial includes polystyrene, a blowing agent that includes an HFCblowing agent, and an infrared attenuating agent that includes graphiteor nanographite. The polyethylene oxide and the copolymer of maleicanhydride and polystyrene have the chemical structures set forth inFormulas I and II:

where n=5-50 and R and R′ are independently H, CH₃, C₂H₅, C₃H₇, or otherhomologs, and

where m=100-2500 and n=100-2500. In at least one exemplary embodiment,the polyethylene oxide is an ethoxylated polyethylene oxide havingFormula III

It is another object of the present invention to provide a foamedproduct that includes an extruded foamable composition comprising afoamable polymer material, at least one blowing agent, an additive blendof polyethylene oxide and a styrene/maleic anhydride copolymer, andoptionally, one or more infrared attenuating agent. The polyethyleneoxide and styrene/maleic anhydride copolymer have the chemicalstructures set forth in Formulas I and II above. In one or moreexemplary embodiment, the polyethylene oxide is an ethoxylatedpolyethylene oxide having Formula III set forth above. The blend ofpolyethylene oxide and styrene/maleic anhydride copolymer increases thewater vapor permeability and increases the average cell size of thefoamed product without detrimentally affecting the physical or thermalproperties of the foamed product. For example, a blend of polyethyleneoxide (e.g., ethoxylated polyethylene oxide) and a styrene/maleicanhydride copolymer provides for a water vapor permeability of 1.1 perminch or greater in the polymer foam product and provides a cell sizefrom about 0.1 mm to about 0.2 mm in the polymer foam product. Inexemplary embodiments, the foamable polymer material includespolystyrene, a blowing agent that includes an HFC blowing agent, and aninfrared attenuating agent that includes nanographite.

It is a further object of the present invention to provide a method offorming a rigid, closed cell foam product that includes heating analkenyl aromatic polymer material and an additive blend of polyethyleneoxide and a copolymer of polystyrene and maleic anhydride, andoptionally, an infrared attenuating agent, to a first temperaturesufficient to melt the polymer material and form a polymer melt,incorporating at least one blowing agent into the polymer melt at afirst pressure to form a foamable gel, cooling the foamable gel to asecond temperature where the second temperature is less than the firsttemperature, and extruding the cooled polymer melt at a pressuresufficient to form a rigid, closed cell extruded foam product. Thepolyethylene oxide and styrene/maleic anhydride copolymer have thechemical structures set forth in Formulas I and II above, respectively.In one or more exemplary embodiment, the polyethylene oxide is anethoxylated polyethylene oxide having Formula III set forth above. Themethod may also include compounding the blend of polyethylene oxide andstyrene/maleic anhydride copolymer in a carrier, pelletizing thecompounded blend of polyethylene oxide and styrene/maleic anhydridecopolymer to form a pellet, and adding the pellet to the polymer melt.

It is an object of the present invention to provide a composition forforming a closed cell, rigid thermoplastic polymer foam that includes astyrene/maleic anhydride copolymer, polyethylene oxide, at least oneblowing agent, and optionally, an infrared attenuating agent. In thisexemplary embodiment, the styrene/maleic anhydride copolymer acts as thefoamable polymer material. It is to be appreciated that in suchembodiments, the foamable composition is free of added polystyreneand/or other (separate) foamable polymer materials. The styrene:maleicanhydride (S:MA) ratio may range from 70:30 (S:MA) to 99:1 (S:MA). Theblowing agent may be selected from hydrofluorocarbons, C₁ to C₉aliphatic hydrocarbons, C₁ to C₃ aliphatic alcohols, carbon dioxide,acetone, natural gases, air, water, ketones, ethers, methyl formate,hydrogen peroxide, and combinations thereof.

It is an advantage of the present invention that an additive blend ofpolyethylene oxide and a copolymer of polystyrene and maleic anhydrideimproves the water vapor permeability and increases the average cellsize of the foamed product without detrimentally affecting the physicalor thermal properties of the product.

It is another advantage of the present invention that the composition ofthe present invention has a low global warming potential and little orno ozone depleting potential.

It is yet another advantage of the present invention that the inclusionof the additive blend in the foamable composition requires nomodification to existing manufacturing equipment and therefore noincrease in manufacturing costs.

It is a further advantage of the present invention that the foamsproduced by the present composition have no toxicity to livingcreatures.

It is yet another advantage of the present invention that an additiveblend of ethoxylated polyethylene oxide and a styrene/maleic anhydridecopolymer provides a water vapor permeability greater than 1.1 perm inchto the extruded foam product.

It is an advantage of the present invention that an additive blend ofethoxylated polyethylene oxide and a styrene/maleic anhydride copolymerprovides a cell size from about 0.10 mm to about 0.20 mm and anR-value/inch from about 5.0 to 7.0 in the extruded foam product.

The foregoing and other objects, features, and advantages of theinvention will appear more fully hereinafter from a consideration of thedetailed description that follows. It is to be expressly understood,however, that the drawings are for illustrative purposes and are not tobe construed as defining the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of this invention will be apparent upon consideration ofthe following detailed disclosure of the invention, especially whentaken in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic illustration of an extrusion apparatus for formingan extruded foam according to at least one exemplary embodiment of theinvention;

FIG. 2 is a graphical illustration of the water vapor permeability (perminch) vs. the percent of added blend of ethoxylated polyethylene oxideand a copolymer of polystyrene and maleic anhydride (actual percent);

FIG. 3 is a graphical illustration of the effect of the additive blendof ethoxylated polyethylene oxide and a copolymer of polystyrene andmaleic anhydride on average cell sizes in an extruded polystyrene foamboard;

FIG. 4 is a graphical illustration of the effect of the additive blendof ethoxylated polyethylene oxide and a copolymer of polystyrene andmaleic anhydride on average cell sizes at 0.5 wt % graphite loading;

FIG. 5 is a graphical illustration of the effect of the additive blendof ethoxylated polyethylene oxide and a copolymer of polystyrene andmaleic anhydride on extrusion pressure;

FIG. 6 is a graphical illustration of the effect of the additive blendof ethoxylated polyethylene oxide and a copolymer of polystyrene andmaleic anhydride on mean cell sizes at 0.5 wt % graphite loading asmeasured by scanning electron microscopy;

FIG. 7 is scanning electron micrograph of a sample of an extrudedpolystyrene foam board containing 0.5 wt % graphite and 0.0 wt % of theadditive blend of ethoxylated polyethylene oxide and a copolymer ofpolystyrene and maleic anhydride;

FIG. 8 is scanning electron micrograph of a sample of an extrudedpolystyrene foam board containing 1.0 wt % graphite and 0.0 wt % of theadditive blend of ethoxylated polyethylene oxide and a copolymer ofpolystyrene and maleic anhydride;

FIG. 9 is scanning electron micrograph of a sample of an extrudedpolystyrene foam board containing 0.5 wt % graphite and 1.5 wt % of theadditive blend of ethoxylated polyethylene oxide and a copolymer ofpolystyrene and maleic anhydride; and

FIG. 10 is scanning electron micrograph of a sample of an extrudedpolystyrene foam board containing 1.0 wt % graphite and 3.0 wt % of theadditive blend of ethoxylated polyethylene oxide and a copolymer ofpolystyrene and maleic anhydride.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the invention belongs. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, the preferred methodsand materials are described herein. All references cited herein,including published or corresponding U.S. or foreign patentapplications, issued U.S. or foreign patents, or any other references,are each incorporated by reference in their entireties, including alldata, tables, figures, and text presented in the cited references. Inthe drawings, the thickness of the lines, layers, and regions may beexaggerated for clarity. It is to be noted that like numbers foundthroughout the figures denote like elements.

The terms “composition” and “inventive composition” may be usedinterchangeably herein. Additionally, the terms “foam board”, “extrudedfoam board”, and “inventive foam board” may be used interchangeablyherein. Further, the terms “increased average cell size” and “enlargedaverage cell size” may be used interchangeably herein. Also, the phrase“copolymer of polystyrene and maleic anhydride” can be interchangeablyused with “styrene/maleic anhydride copolymer”.

The present invention relates to polymer extruded or expanded foams thatcontain an additive blend of polyethylene oxide and a copolymer ofpolystyrene and maleic anhydride (“additive blend”) as both a watervapor permeability enhancing agent to increase the water vaporpermeability of the foamed product and as a cell size enlarging agent toincrease the average cell size of the foamed product. The additive blendof a polyethylene oxide and styrene/maleic anhydride copolymer increasesthe water vapor permeability and cell size of the foamed product withoutdetrimentally affecting the physical or thermal properties of theproduct formed. The composition used to form extruded (or expanded)foams having an improved water vapor permeability and an increased cellsize includes a foamable polymer material, at least one blowing agent(e.g., hydrofluorocarbon (HFC)), a blend of a polyethylene oxide and astyrene/maleic anhydride copolymer, and, in exemplary embodiments, aninfrared attenuating agent (e.g., graphite or nanographite). Theadditive blend of a polyethylene oxide and styrene/maleic anhydridecopolymer acts as a process aid and a plasticizer, enhances thesolubility of the blowing agent, and lowers the die pressure.

The foamable polymer material is the backbone of the formulation andprovides strength, flexibility, toughness, and durability to the finalproduct. The foamable polymer material is not particularly limited, andgenerally, any polymer capable of being foamed may be used as thefoamable polymer in the resin mixture. The foamable polymer material maybe thermoplastic or thermoset. The particular polymer material may beselected to provide sufficient mechanical strength and/or to the processutilized to form final foamed polymer products. In addition, thefoamable polymer material is preferably chemically stable, i.e.,generally non-reactive, within the expected temperature range duringformation and subsequent use in a polymeric foam. Non-limiting examplesof suitable foamable polymer materials include alkenyl aromaticpolymers, polyvinyl chloride (PVC), chlorinated polyvinyl chloride(CPVC), polyethylene, polypropylene, polycarbonates, polyisocyanurates,polyetherimides, polyamides, polyesters, polycarbonates,polymethylmethacrylate, polyphenylene oxide, polyurethanes, phenolics,polyolefins, styreneacrylonitrile (SAN), acrylonitrile butadienestyrene, acrylic/styrene/acrylonitrile block terpolymer (ASA),polysulfone, polyurethane, polyphenylenesulfide, acetal resins,polyamides, polyaramides, polyimides, polyacrylic acid esters,copolymers of ethylene and propylene, copolymers of styrene andbutadiene, copolymers of vinylacetate and ethylene, rubber modifiedpolymers, thermoplastic polymer blends, and combinations thereof.

In one exemplary embodiment, the foamable polymer material is an alkenylaromatic polymer material. Suitable alkenyl aromatic polymer materialsinclude alkenyl aromatic homopolymers and copolymers of alkenyl aromaticcompounds and copolymerizable ethylenically unsaturated comonomers. Inaddition, the alkenyl aromatic polymer material may include minorproportions of non-alkenyl aromatic polymers. The alkenyl aromaticpolymer material may be formed of one or more alkenyl aromatichomopolymers, one or more alkenyl aromatic copolymers, a blend of one ormore of each of alkenyl aromatic homopolymers and copolymers, or blendsthereof with a non-alkenyl aromatic polymer. Notwithstanding thecomponents of the composition, the alkenyl aromatic polymer material mayinclude greater than 50 or greater than 70 weight percent alkenylaromatic monomeric units. In at least one embodiment of the invention,the alkenyl aromatic polymer material is formed entirely of alkenylaromatic monomeric units.

Examples of alkenyl aromatic polymers include, but are not limited to,those alkenyl aromatic polymers derived from alkenyl aromatic compoundssuch as styrene, α-methylstyrene, ethylstyrene, vinyl benzene, vinyltoluene, chlorostyrene, and bromostyrene. In at least one embodiment,the alkenyl aromatic polymer is polystyrene.

Minor amounts of monoethylenically unsaturated compounds such as C₂ toC₆ alkyl acids and esters, ionomeric derivatives, and C₂ to C₆ dienesmay be copolymerized with alkenyl aromatic compounds. Non-limitingexamples of copolymerizable compounds include acrylic acid, methacrylicacid, ethacrylic acid, maleic acid, itaconic acid, acrylonitrile, maleicanhydride, methyl acrylate, ethyl acrylate, isobutyl acrylate, n-butylacrylate, methyl methacrylate, vinyl acetate and butadiene.

The foamed products may be formed substantially of (e.g., greater than95 percent), and in most embodiments, formed entirely of polystyrene.The foamable polymer material may be present in the composition in anamount from about 60% to about 95% by weight, in an amount from about70% to about 90% by weight, or in an amount of about 85% to about 90% byweight. In exemplary embodiments, the foamable polymer material may bepresent in an amount from about 90% to about 95% by weight. As usedherein, the term “% by weight” is meant to indicate a percentage basedon 100% of the total weight of the dry components.

It is to be appreciated that the properties of the extruded foam or foamproduct may be modified by the selection of the molecular weight of thepolymer. For example, the preparation of lower density extruded foamproducts is facilitated by using lower molecular weight polymers. On theother hand, the preparation of higher density extruded foam products isfacilitated by the use of higher molecular weight polymers or higherviscosity resins.

The foamable composition may include at least one hydrofluorocarbon(HFC) blowing agent. The specific hydrofluorocarbon utilized is notparticularly limited. A non-exhaustive list of examples of suitableblowing HFC blowing agents include 1,1-difluoroethane (HFC-152a),difluoroethane (HFC-152), 1,1,1,2-tetrafluoroethane (HFC-134a),1,1,2,2-tetrafluoroethane (HFC-134), 1,1,1-trifluoroethane (HFC-143a),difluoromethane (HFC-32), 1,3,3,3-pentafluoropropane (HFO-1234ze),pentafluoro-ethane (HFC-125), fluoroethane (HFC-161),1,1,2,2,3,3-hexafluoropropane (HFC 236ca), 1,1,1,2,3,3-hexafluoropropane(HFC-236ea), 1,1,1,3,3,3-hexafluoropropane (HFC-236fa),1,1,1,2,2,3-hexafluoropropane (HFC-245ca), 1,1,2,3,3-pentafluoropropane(HFC-245ea), 1,1,1,2,3 pentafluoropropane (HFC-245eb),1,1,1,3,3-pentafluoropropane (HFC-245fa), 1,1,1,4,4,4-hexafluorobutane(HFC-356mff), 1,1,1,3,3-pentafluorobutane (HFC-365mfc), FEA-1100(DuPont), 2,3,3,3-tetrafluoroprop-1-end (R-1234YF from Arkema), andcombinations thereof.

Other blowing agents useful in the practice of this invention includeinorganic blowing agents, organic blowing agents, and chemical blowingagents. Any suitable blowing agent may be used in the practice on thisinvention as a blowing agent. However, due to increased environmentalconcern over global warming and ozone depletion, in exemplaryembodiments, the foamable composition is free of blowing agentscontaining chlorofluorocarbons (CFCs).

Non-limiting examples of organic blowing agents suitable for use in thepresent invention include C₂ to C₉ aliphatic hydrocarbons (e.g.,methane, ethane, propane, n-butane, cyclopentane, isobutane, n-pentane,isopentane, and neopentane), C₁ to C₅ aliphatic and non-aliphaticalcohols (e.g., methanol, ethanol, n-propanol, isopropanol, andbutanol). Natural gases such as carbon dioxide (CO₂), nitrogen (N₂),and/or argon (Ar) may also be used as a blowing agent. Water, air,ketones (e.g., acetone and methyl ethyl ketone), ethers (e.g., dimethylethers and diethyl ethers), methyl formate, acetone, and hydrogenperoxide may also be used as blowing agents. The blowing agentsidentified herein may be used singly or in combination. In exemplaryembodiments, the blowing agent includes at least one hydrofluorocarbon(HFC) blowing agent. The blowing agent may be present in the compositionin an amount from about 4.0% to about 10.0% by weight, and in exemplaryembodiments, from about 4.0% to about 8.5% by weight, or from about 7.5%to about 8.0% by weight, or from about 7.6% to about 7.9% by weight. Theblowing agent utilized in the inventive composition is selected suchthat the composition has zero ozone depletion and low to no globalwarming potential. In at least one exemplary embodiment, the blowingagent is 1,1-difluoroethane (HFC-152a), 1,1,1,2-tetrafluoroethane(HFC-134a), or a combination of 1,1-difluoroethane (HFC-152a) and1,1,1,2-tetrafluoroethane (HFC-134a).

As discussed above, the composition may also contain at least oneinfrared attenuating agent to increase the R-value of the foam product.Hydrofluorocarbon blowing agents, while environmentally friendly, tendto decrease the R-value of the foam product compared to a conventionalHCFC foamed product (e.g., R-value per inch of 5.0) at comparabledensities. As taught in U.S. Patent Publication Number 2008/0242752 toDelaviz, et al., which is incorporated herein by reference in itsentirety, it was discovered that the addition of low levels of aninfrared attenuating agent to a foamable composition containing ahydrofluorocarbon blowing agent increased the R-value of the foam to anamount comparable to, or better than, a foam produced with an HCFCblowing agent (e.g., 1-chloro-1,1-difluoroethane (HCFC-142b)).

It was also discovered that, generally, foams produced with an infraredattenuating agent and a hydrofluorocarbon blowing agent had an R-valueper inch of 5.0 or greater. Non-limiting examples of suitable infraredattenuating agents for use in the present composition include graphite,nanographite, carbon black, powdered amorphous carbon, asphalt,granulated asphalt, milled glass, fiber glass strands, mica, black ironoxide, metal flakes (e.g., aluminum flakes), carbon nanotube,nanographene platelets, carbon nanotubes (both single and multi-walled),carbon nanofiber, activated carbon, metal oxides (e.g., titaniumdioxide, aluminum oxide, etc.), and combinations thereof. As used inconjunction with this invention, “nano” compounds, such as, for example,“nanographite”, are intended to denote compounds that have a thicknessin at least one dimension, most likely the thickness of the particle, ofless than about 100 nanometers. In exemplary embodiments, the infraredattenuating agent is present in the foam composition in an amount fromabout 0% to about 5.0% by weight of the total dry components of thecomposition. In other embodiments, the infrared attenuating agent may bepresent in an amount from about 0.01% to about 5.0% by weight, fromabout 0.05% to about 1.0% by weight, or in an amount of about 0.1% toabout 0.5% by weight.

Although the infrared attenuating agent increases the R-value for foamsthat include hydrofluorocarbon blowing agents, the addition of infraredattenuating agents also tends to decrease the cell size of the cells inthe foam, which results in undesirable final foamed products. Inparticular, small cell sizes tend to increase board bulk density,increase product cost, and reduce the process window during theextrusion process. Further, infrared attenuating agents undesirablyincrease the melt rheology, which will result in an increase of the diepressure.

In addition, although the use of non-CFC blowing agents reduces oreliminates ozone depletion and non-CFC blowing agents have a low to noglobal warming potential, they do not provide a significant improvementin the water vapor permeability over conventional CFC blowing agents. Asused herein, “water vapor permeability” is meant to denote the abilityof moisture (e.g., water vapor) to pass through the foam board. Havingproper or adequate water vapor permeability reduces or eliminates thepotential for condensation and/or mold and fungal growth on the foamedboards and/or in the wall system in which the foam boards are used. Asis known in the art, mold and fungal growth may cause undesirable odor,discoloration, and/or product deterioration. A higher water vaporpermeability enhances the performance of the foam board, therebyallowing water vapor to migrate through the board (and thus the buildingwall), minimizing or eliminating the occurrence of condensation andmold/fungal growth.

Closed cell extruded foam boards formed using CFC blowing agents, suchas HCFC-142b, typically have a water vapor permeability of 1.0 perm inchor less. It has been determined that foam boards produced with HFCblowing agents, such as HFC-134a and/or HFC-152a, and/or CO₂ do not havea significant impact on improving the water vapor permeability of foamboard, as these boards also typically have a water vapor permeability ofless than about 1.0 perm inch. To improve the water vapor permeabilityof foamed boards formed with non-CFC blowing agents and/or to compensatefor the decreased cell size caused by the infrared attenuating agent andthe blowing agent (e.g., HFC-134a and/or HFC-152a and/or CO₂), a blendof (1) a polyethylene oxide and (2) a copolymer of maleic anhydride andpolystyrene having the chemical structures set forth in Formulas I andII may be included in the foamable composition:

where n=5-50 and R and R′ are independently H, CH₃, C₂H₅, C₃H₇, or otherhomologs, and

where m=100-2500 and n=100-2500. It is to be appreciated that foamsproduced utilizing the inventive composition containing the additiveblend can be used in markets that desire improved water vaporpermeability and/or in markets that desire increased cell size.

As noted above, the polyethylene oxide can be end-capped with alkoxygroups such as methoxy, ethoxy, propyloxy, butoxy, as well as otherhomologs compounds. Although any of these homologs of polyethylene oxideare suitable for use in the inventive composition, reference will bemade herein to ethoxylated polyethylene oxide, which has the formula setforth in Formula III

where n=5-50.

It has been surprisingly discovered that the addition of the additiveblend of ethoxylated polyethylene oxide and a copolymer of maleicanhydride and polystyrene in an amount of as little as 1.0% by weightproduces a foam board having a water vapor permeability that is greaterthan 1.1 perm inch. Additionally, it has been discovered that theaddition of as low as 1.0% by weight of a blend of ethoxylatedpolyethylene oxide and a styrene/maleic anhydride copolymer in thefoamable composition results in an enhancement of the water vaporpermeability by more than 50%. The addition of thepolystyrene/polyethylene oxide copolymer to the foamable compositionprovides a water vapor permeability of greater than 1.1 perm inch, andin exemplary embodiments, from 1.1 perm inch to 1.5 perm inch, from 1.2perm inch to 1.5 perm inch, or from 1.3 perm inch to 1.5 perm inchwithout an adverse and/or negative impact on the general physical andthermal properties of the extruded foam board.

It has also been surprisingly discovered that the additive blend ofethoxylated polyethylene oxide and a copolymer of maleic anhydride andpolystyrene increases the cell size of the polymer foam and offsets oreven negates the decreased cell size caused by the HFC blowing agentand/or the infrared attenuating agents. In addition, the blend ofethoxylated polyethylene oxide and a copolymer of maleic anhydride andpolystyrene has a positive affect on the processability of the HFCblowing agent(s) in the composition by both widening the process windowand enhancing the HFC solubility in the polymer melt. Thus, the additiveblend of ethoxylated polyethylene oxide and a styrene/maleic anhydridecopolymer present in the inventive composition acts as a cell enlarger,a plasticizer, and a processing aid. Further, the polyethylene oxidemoieties add polarity to the polymer melt and help to improve thesolubility of HFC blowing agents (e.g., HFC-134a, HFC-152a, and CO₂).Due to the plasticizing effect of the blend of ethoxylated polyethyleneoxide and a copolymer of maleic anhydride and polystyrene, free volumeis created in the melt, which results in higher blowing agent solubilityand a lowering of the melt viscosity.

The use of the blend of ethoxylated polyethylene oxide and astyrene/maleic anhydride copolymer in conjunction with the infraredattenuating agent permits the formation of a foam with an optimized cellsize and a high insulation value (R-value) and to optimize the physicalproperties of the final foamed product. In addition, the blend ofethoxylated polyethylene oxide and a copolymer of maleic anhydride andpolystyrene provides an increased cell size to the foamed productwithout detracting from the physical and thermal properties the foam. Itis believed that the blowing agent(s) and the infrared attenuatingagent(s) have a synergistic affect on the cell morphology and decreasein cell size that is surprisingly overcome by the addition of the blendof ethoxylated polyethylene oxide and a copolymer of maleic anhydrideand polystyrene.

In addition, the inclusion of an infrared attenuating agent in thefoamable composition has no significant impact on the improvement of thewater vapor permeability of the extruded foam boards caused by theadditive blend of ethoxylated polyethylene oxide and a styrene/maleicanhydride copolymer. Thus, foams produced with an infrared attenuatingagent, a hydrofluorocarbon blowing agent, and the blend of ethoxylatedpolyethylene oxide and a copolymer of maleic anhydride and polystyrenehave both an increased R-value per inch and an increased water vaporpermeability.

The blend of ethoxylated polyethylene oxide and a styrene/maleicanhydride copolymer may be added to the composition in an amount fromabout 0.5% to about 5.0% by weight, particularly from about 1.0% toabout 4.0% by weight, and in exemplary embodiments, from about from 1.0%to about 3.0% by weight of the total dry components of the composition.

Further, the inventive composition may contain a fire retarding agent inan amount up to about 1.0% by weight. For example, fire retardantchemicals may be added in the extruded foam manufacturing process toimpart fire retardant characteristics to the extruded foam products. Inexemplary embodiments, the fire retarding agent is added to the foamablegel, which is described below with respect to the formation of theinventive foam. Non-limiting examples of suitable fire retardantchemicals for use in the inventive composition include brominatedaliphatic compounds such as hexabromocyclododecane andpentabromocyclohexane, brominated phenyl ethers, esters oftetrabromophthalic acid, and combinations thereof.

Optional additives such as nucleating agents, plasticizing agents,pigments, elastomers, extrusion aids, antioxidants, fillers, antistaticagents, biocides, and/or UV absorbers may be incorporated into theinventive composition. These optional additives may be included inamounts necessary to obtain desired characteristics of the foamable gelor resultant extruded foam products. The additives may be added to thepolymer mixture or they may be incorporated in the polymer mixturebefore, during, or after the polymerization process used to make thepolymer.

In one exemplary embodiment, the foamable polymer material is omittedfrom the composition and the styrene/maleic anhydride copolymer from theadditive blend acts as the foamable polymer material. In this instance,the styrene:maleic anhydride (S:MA) ratio may range from 70:30 (S:MA) to99:1 (S:MA), or from 70:30 to 95:5 (S:MA). It is to be appreciated thatin such embodiments, the foamable composition is free of additionalpolystyrene and/or other (separate) foamable polymer materials. Theremainder of the inventive composition remains the same as thatdescribed in detail above, and includes the polyethylene oxide presentin the additive blend as the cell size enhancer and water vaporpermeability enhancer, one or more blowing agents, and optionally,infrared attenuating agent(s), flame retardant(s), and/or otheradditives.

To form an extruded polymer foam according to the principles of theinstant invention, the foamable polymer material (e.g., polystyrene) maybe heated to a temperature at or above the polymer's glass transitiontemperature or melting point to form a plasticized or a melt polymermaterial. The infrared attenuating agent (e.g., nanographite) may beblended in the polymer melt or dry blended with the polymermaterial/carrier prior to plasticizing or melting the foamable polymermaterial. It is to be appreciated that nanographite may also be addeddirectly as a powder, in a compact form, or in a slurry. The blend ofethoxylated polyethylene oxide and copolymer of polystyrene and maleicanhydride may be compounded in a carrier such as polystyrene,pelletized, and added to the polymer melt, such as is demonstrated inthe examples below. Alternatively, the additive blend of ethoxylatedpolyethylene oxide and styrene/maleic anhydride copolymer may be addeddirectly, may use other carriers/polymers, or may be dissolved in asolvent such as alcohol and added to the extrusion as a liquid using apump.

It is noted that in an embodiment where the styrene maleic anhydridecopolymer is utilized as the foamable polymer material, the procedurefor forming the polymer melt is the same as set forth above with theexception that the styrene maleic anhydride copolymer is substituted forthe polystyrene and the additive blend consists of the polyethyleneoxide.

One or more blowing agents (e.g., 1,1-difluoroethane (HFC-152a) and/or1,1,1,2-tetrafluoroethane (HFC-134a)) is incorporated or mixed into themelt polymer material by any conventional method known to those of skillin the art such as, for example, with an extruder, a mixer, or ablender. As the blowing agent is added to the polymer melt, the blowingagent becomes soluble, i.e. dissolves, in the polymer melt and forms afoamable gel. Additionally, the blowing agent may be mixed with the meltpolymer material at an elevated pressure sufficient to preventsubstantial expansion of the melt polymer material and to generallydisperse the blowing agent(s) substantially homogeneously orheterogeneously in the melt polymer material.

The foamable gel may then be cooled to a die melt temperature. The diemelt temperature is typically cooler than the melt mix temperature tooptimize the physical characteristics of the foamed product. Inaddition, that the die pressure may be sufficient to prevent, or atleast minimize, pre-foaming of the foamable gel. Pre-foaming is theundesirable premature foaming of the foamable gel before extrusion ofthe gel into a region of reduced pressure. Thus, the die pressure variesdepending upon the identity and amount of blowing agent(s) present inthe foamable gel. The foamable gel may then be extruded through a diehaving a desired shape to a zone of lower or reduced pressure to formthe desired foamed structure or foamed product. The zone of lowerpressure is at a pressure lower than that in which the foamable gel ismaintained prior to extrusion through the die. The lower pressure may besuperatmospheric or subatmospheric (i.e., a vacuum), but in mostembodiments, it is at atmospheric level. The foam thus produced is arigid, closed cell, polymer foam.

A screw extruder for use in the present invention is generally indicatedat reference numeral 10 in FIG. 1. The screw extruder for use in theinstant invention may equally be a single screw or twin screw extruder.Reference is made herein with respect to a single screw extruder. Theextruder 10 is formed of a barrel 12 and at least one screw 14 thatextends substantially along the length of the barrel 12. A motor (M) maybe used to power the screw 14. The screw 14 contains helical flights 16rotating in the direction of arrow 18. The flights 16 of the screw 14cooperate with the cylindrical inner surface of the barrel 12 to definea passage for the advancement of the resin and reinforcement fibersthrough the barrel 12. The foamable polymer material may be fed into thescrew extruder 10 as flowable solid, such as beads, granules, or pelletsfrom one or more feed hoppers 20.

As the foamable polymer material flows through the extruder 10 in thedirection of arrow 18, the spacing between the flights 16 of the screw14 decreases. Thus, the volume between the flights 16 decreases as thepolymer melts flows downstream. The term “downstream” as used hereinrefers to the direction of resin and fiber flow through the barrel 12.This decreasing volume, together with the mechanical action and frictiongenerated from the barrel 12 and the screw 14, causes the foamablepolymer material to melt and form the melt polymer material.

It is to be appreciated that the flights 16 of the screw 14 cooperatewith the cylindrical inner surface of the barrel 12 to define a passagefor the advancement of the polymer melt through the barrel 12. As shownin FIG. 1, ports are provided at designated positions on the extruderfor the insertion of the infrared attenuating agent, the blend ofethoxylated polyethylene oxide and a copolymer of polystyrene and maleicanhydride, and for the injection of the blowing agent(s). Specifically,a hopper 22 is provided downstream of the feed hopper 20 to feed theinfrared attenuating agent into the barrel 12. The infrared attenuatingagent and the additive blend of ethoxylated polyethylene oxide and astyrene/maleic anhydride copolymer are mixed into the polymer melt bythe rotation of the screw 14. It is to be noted, however, that otherports and/or hoppers may be present on the barrel 12 for the inclusionof other materials or additives, such as, but not limited to, flameretardants, nucleating agents (e.g., talc), biocides, plasticizingagents, pigments, elastomers, extrusion aids, antioxidants, fillers,and/or antistatic agents.

In at least one embodiment, the resin and the blend of ethoxylatedpolyethylene oxide and a copolymer of polystyrene and maleic anhydrideare substantially simultaneously fed into the barrel 12 of the extruder10 through feed hopper 22. As used herein, the term “substantiallysimultaneously fed” is meant to indicate that the polymer resin and theblend of ethoxylated polyethylene oxide and a copolymer of polystyreneand maleic anhydride are fed into the barrel 12 at the same time or atnearly the same time.

Once the infrared attenuating agent, blowing agent(s), and the additiveblend of ethoxylated polyethylene oxide and a styrene/maleic anhydridecopolymer have been introduced into the barrel 12, the resultingfoamable mixture is subjected to additional blending to substantiallyuniformly distribute the infrared attenuating agent, blowing agent, andthe blend of ethoxylated polyethylene oxide and a styrene/maleicanhydride copolymer throughout the foamable mixture.

The heat from the internal friction from the screw 14 within the barrel12 causes the blowing agent to be uniformly or substantially uniformlydispersed for improved solubility. The foamable mixture is subsequentlycooled to a lower temperature in a melt cooler 25 and then conveyed fromthe extruder 10 through an extrusion die 26 which is designed to shapethe foam into a desired shape and to create a pressure drop whichpermits the blowing agent to expand and develop a foamed cell structurein the form of a foam layer or slab. In particular, the foamable mixtureenters an area of reduced pressure as it exits the die. The polymericfoam may be subjected to additional processing such as calendaring,water immersion, cooling sprays, post-steaming, or other operations tocontrol the thickness and other properties of the resulting foamproduct.

The foam composition produces rigid, closed cell, polymer foam boardsprepared by an extruding process. Extruded foams have a cellularstructure with cells defined by cell membranes and struts. Struts areformed at the intersection of the cell membranes, with the cellmembranes covering interconnecting cellular windows between the struts.In the present invention, the inventive composition producessubstantially closed cellular foams with an average density of about 1.3lbs/ft³ to about 3.0 lbs/ft³, from about 1.5 lbs/ft³ to about 4.0lbs/ft³, or from about 1.3 lbs/ft³ to about 4.0 lbs/ft³. It is to beappreciated that the phrase “substantially closed cell” is meant toindicate that the foam contains all closed cells or nearly all of thecells in the cellular structure are closed. In most exemplaryembodiments, not more than about 5.0% of the cells are open cells. Theclosed cell structure helps to increase the R-value of a formed, foamedinsulation product. It is to be appreciated, however, that it is withinthe purview of the present invention to produce an open cell structure,although such an open cell structure is not an exemplary embodiment.

Additionally, the inventive foam composition produces extruded foamsthat have insulation values (R-values) that are equal to or better thanconventional extruded foams produced with 1-chloro-1,1-difluoroethane(HCFC-142b). The R-value per inch of the inventive foams and foamproducts may be from 5.0 to 7.0. In at least one embodiment, the R-valueper inch is from 5.0 to 6.0. In addition, the average cell size of theinventive foam and foamed products is about 0.1 mm to about 0.2 mm, orfrom about 0.14 mm to about 0.16 mm. In some embodiments, the averagecell size is from about 0.12 mm to about 0.16 mm. The extruded inventivefoam may be formed into an insulation product such as rigid insulationboards, insulation foam, packaging products, and building insulation orunderground insulation (e.g., highway, airport runway, railway, andunderground utility insulation).

Another aspect of the extruded inventive foams is that they possess ahigh level of dimensional stability. For example, the change indimension in any direction is about 5% or less. In addition, the foamformed by the inventive composition is desirably monomodal and the cellshave a relatively uniform average cell size. As used herein, the averagecell size is an average of the cell sizes as determined in the X, Y andZ directions. In particular, the “X” direction is the direction ofextrusion, the “Y” direction is the cross machine direction, and the “Z”direction is the thickness. In the present invention, the highest impactin cell enlargement is in the X and Y directions, which is desirablefrom an orientation and R-value perspective. In addition, furtherprocess modifications would permit increasing the Z-orientation toimprove mechanical properties while still achieving an acceptablethermal property. The extruded inventive foam can be used to makeinsulation products such as rigid insulation boards, insulation foam,and packaging products.

There are numerous advantages of utilizing the composition of thepresent invention to form foam products. For example, the blowing agentutilized in the inventive formulation has a lower global warmingpotential than current HFC-142b and has zero ozone depleting potential.In addition, the infrared attenuating agent and the additive blend ofethoxylated polyethylene oxide and copolymer of polystyrene and maleicanhydride may be added to the melt polymer in a conventional fashion.Therefore, in at least some exemplary embodiments, there is no need tomodify existing equipment or change the manufacturing lines toaccommodate either the infrared attenuating agent or the blend ofethoxylated polyethylene oxide and styrene/maleic anhydride copolymer.In addition, the blend of ethoxylated polyethylene oxide andstyrene/maleic anhydride copolymer is environmentally friendly and doesnot create any negative environmental concerns. Further, the blend ofethoxylated polyethylene oxide and styrene/maleic anhydride copolymerincreases the water vapor permeability and increases the average cellsize of the foamed product without detrimentally affecting the physicalor thermal properties of the product. Additionally, the addition of theblend of ethoxylated polyethylene oxide and styrene/maleic anhydridecopolymer improves the overall surface quality of the foam.

Additionally, the blend of ethoxylated polyethylene oxide andstyrene/maleic anhydride copolymer improves the solubility of the HFCblowing agent(s) in the foamable composition. The blend of ethoxylatedpolyethylene oxide and styrene/maleic anhydride copolymer acts as aplasticizer to reduce the melt viscosity and lower the extrusionpressures. Also, the presence of maleic anhydride as well aspolyethylene oxide moieties provides polarity through the C—CO—C andC—O—C bonds in the matrix, resulting in an improved solubility ofblowing agents such as HFC-134a, HFC-152a, and CO₂. Additionally,through the plasticization, the polyethylene oxide moieties create freevolume in the matrix, which results in higher blowing agent solubilityand a lowered melt viscosity. Overall, the blend of ethoxylatedpolyethylene oxide and styrene/maleic anhydride copolymer acts asprocess aid and, as is demonstrated in the following examples, lowersthe extrusion pressure.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples illustrated belowwhich are provided for purposes of illustration only and are notintended to be all inclusive or limiting unless otherwise specified.

EXAMPLES Water Vapor Permeability

Compositions containing polystyrene, a mixture of HFC-134a/HFC-152a asblowing agents, graphite, and a blend of ethoxylated polyethylene oxideand styrene/maleic anhydride copolymer (Additive Blend) as depicted inTable 1 were formed and used to generate foam board samples. Inparticular, nanographite was compounded at 20% active in general purposepolystyrene with the following characterics; Mw 253000, Mn 61300, Mz532500, Mw/Mn (polydispersity) 3.44. The Additive Blend was compoundedin general purpose polystyrene at 0.5%, 1/0%, 1.5%, 2.0%, 4%, 6%, 8%,10%, and 12% active. The blowing agent utilized was a 50:50 blend ofHFC-134a/HFC-152a at 7.5 wt % based on the resin weight. Foam boardswere formed from the composition on an Owens Corning horizontal pilotline extrider at a 160 kg/hour dry throughput rate.

TABLE 1 Water Additive Vapor Blowing Additive Blend Blend GraphiteGraphite Flame Perm Agent (Compounded) (Actual) (Compounded) (Actual)Retardant (Perm Sample (%) (%) (%) (%) (%) (%) Inch) 1 7.5 0.0 0.0 2.50.5 1.0 1.021 2 7.5 0.5 0.13 2.5 0.5 1.0 0.975 3 7.5 1.0 0.25 2.5 0.51.0 0.975 4 7.5 1.5 0.38 2.5 0.5 1.0 0.988 5 7.5 2.0 0.50 2.5 0.5 1.01.011 6 7.5 4.0 1.00 2.5 0.5 1.0 1.497 7 7.5 6.0 1.50 2.5 0.5 1.0 1.4318 7.5 8.0 2.00 2.5 0.5 1.0 1.428 9 7.5 10.0 2.50 2.5 0.5 1.0 1.481 107.5 12.0 3.00 2.5 0.5 1.0 1.447

Once the foam boards were made, the water vapor permeability of theboards were tested according to the procedure set forth in ASTM E-96(Standard Test Method For Water Vapor Transmission Of Materials(Dessicant Method)). The test method involves filling a non-permeabletest dish with desiccant to within ¼ inch of the specimen. The perimeterof the dish is sealed to prevent vapor diffusion either into or out ofthe dish. The dish containing the specimen and the desiccant is thenplaced in a temperature and humidity controlled room and weighedperiodically until a steady state weight gain is achieved. The watervapor permeability is then calculated from the obtained data. Theresults are depicted in FIG. 2.

As shown in FIG. 2, the addition of the blend of ethoxylatedpolyethylene oxide and styrene/maleic anhydride copolymer in amounts aslow as 1.0% caused a significant increase in the water vaporpermeability of the foamed boards. Amounts from about 1.0% to about 3.0%of the blend of ethoxylated polyethylene oxide and styrene/maleicanhydride copolymer had a significant improvement in water vaporpermeability. It was also noted that there was no significant increasein the water vapor permeability as additional ethoxylated polyethyleneoxide and styrene/maleic anhydride copolymer was added to the polymermix over about 3%.

Inclusion of a Blend of Ethoxylated Polyethylene Oxide andStyrene/Maleic Anhydride Copolymer in an Extruded Polystyrene Foam Board

Compositions containing polystyrene, a mixture of HFC-134a/HFC-152a asblowing agents, graphite, and a blend of ethoxylated polyethylene oxideand styrene/maleic anhydride copolymer (Additive Blend) as depicted inTable 2 were formed and used to generate foam board samples. Inparticular, nanographite was compounded at 20% active in general purposepolystyrene with the following characterics; Mw 201800, Mn 53900, Mz407600, Mw/Mn (polydispersity) 3.4 and melt flow index of 10.7 (asdetermined using ASTM D1238 condition G). The blend of ethoxylatedpolyethylene oxide and styrene/maleic anhydride copolymer was compoundedin general purpose polystyrene at 25% active. The blowing agent utilizedwas a 50:50 blend of HFC-134a/HFC-152a at 7.0 wt % based on the resinweight. Foam boards were formed from the composition on an Owens Corninghydrovac horizontal pilot line extrusion at a 160 kg/hour throughputrate.

TABLE 2 Graphite Additive Blend (20%) (25%) Ave. % added/ % added/Density X-cell Y-cell Z-cell Cell Orientation Sample actual % actual %(pcf) (mm) (mm) (mm) (mm) X:Z Control 1 2.5/0.5  0/0 1.77 0.110 0.1200.120 0.117 0.92:1 1 2.5/0.5 4.00/1.0 1.68 0.120 0.110 0.120 0.1200.94:1 2 2.5/0.5  6.0/1.5 1.63 0.127 0.136 0.140 0.134 0.91:1 3 2.5/0.512.0/3.0 1.93 0.142 0.149 0.146 0.148 0.97:1 4 2.5/0.5 12.0/3.0 1.620.153 0.170 0.161 0.161 0.96:1

The following was noted and/or concluded from Table 2:

-   -   Control 1 had 0.5% actual graphite in the foamable composition.        In addition, Control 1 did not contain any Additive Blend. The        average cell size for Control 1 was 0.117 mm.    -   Samples 1, 2, 3, and 4 contained the same graphite loading and        increasing levels of the Additive Blend as a cell enlarger. When        3.0% actual Additive Blend was added as shown in Samples 3 and        4, the average cell increased to 0.146 mm and 0.161 mm        respectively. It was determined that this was an approximately        38% increase in the average cell size (over the control) when        3.0% Additive Blend is added. It was noted that Sample 3 had a        much higher density (i.e., 1.93 pcf), and it is believed that        this higher density explains why the average cell for Sample 3        was 0.148 mm, and not closer to 0.161 mm as in Example 4.    -   Sample 1, which contained a 1.0% Additive Blend, had essentially        no effect on the average cell size over the Control sample. It        was noted that Sample 1 was much closer in density to Sample 4        and it was therefore believed to explain why higher levels of        the Additive Blend in the foamable composition acted as a cell        enlarger at comparable densities.    -   There is a larger effect of the Additive Blend on the average        cell sizes in the presence of 0.5 wt % graphite, as is        graphically illustrated in FIGS. 3 and 4.

TABLE 3 Additive Static Graphite (20%) Blend (25%) Extrusion Mix Die %added/ % added/ Out Out Pressure Sample actual % actual % (bars) (bars)(bars) Control 2 5.0/1.0 0/0 232.6 163.2 61.00 1 5.0/1.0 2.0/0.5 216.7157.7 64.17 2 5.0/1.0 4.0/1.0 213.8 155.3 67.02 3 5.0/1.0 6.0/1.5 202.3150.8 67.34

The following was noted and/or concluded from Table 3:

-   -   Comparing the Control having 0% PEO additive with Sample 3        having 1.5% of the Additive Blend, it can be seen that there is        13% and 8% reduction in extrusion and static mixture pressures,        respectively. The effect of the Additive Blend on extrusion        pressure was more pronounced in the presence of 1.0 wt %        graphite as shown in Table 3 and illustrated in FIG. 5. The        extrusion pressure was 232.6 and 202.30 bars at the 0.0 and 1.5        wt % the Additive Blend, respectively. The overall lower        extrusion pressure equated to better processability and a wider        process window. It was concluded that the plasticization effect,        polarity, and hydrophilicity of the Additive Blend enhanced the        HFC-134a and HFC-152a solubility in the polystyrene melt,        lowered viscosity, and reduced the overall pressures of the        extrusion process.    -   It was noted that there were not any adverse and/or negative        impact on the general physical and thermal properties of the        extruded foam board when the Additive Blend was used in the        foamable composition.

Scanning Electron Microscopy (SEM)

The cell morphology of the foam board formed above was also studiedusing scanning electron microscopy (SEM). This methodology (i.e., theSEM) shoes the impact of the Additive Blend on the average cell sizes isdepicted both in Table 4 and in FIG. 6. The average cell sizes were0.113 mm and 0.203 mm in the presence of 0.0 and 3.0 wt % of theAdditive Blend, respectfully. This was calculated to be an approximate80% increase in cell size.

TABLE 4 Mean Cell Sizes Measured By SEM Graphite Additive Blend MeanCell Sample Wt % actual Wt % actual Sizes mm Control 1 0.5 0 0.113Sample 2 0.5 1.5 0.180 Sample 4 0.5 3.0 0.203

The SEM analysis of the extruded boards showed that as the cells becomelarger, the cell wall thickness and strut diameter generally becomesmaller, as is shown in Table 7.

TABLE 5 Cell Wall Additive Total Struts Graphite Blend Cell Cell Ave.Total Ave. Wt % Wt % Cells/ Wall/ Walls Std. Struts/ Struts Std. Sampleactual actual mm² mm Counted Dev. mm² Counted Dev. Control 1 0.5 0 11312 24 0.9/0.41 170 170 3.5/1.02 Sample 1 1.0 1.0 112 12.5 25 0.6/0.21172 172 2.6/0.63 Sample 2 0.5 1.5 71 8.0 16 1.0/0.35 106 106 4.7/0.92Sample 4 0.5 3.0 61 8.0 16 1.4/0.74 106 106 5.3/2.05

The impact of the Additive Blend on cell morphology in the presence of0.5 and 1.0 wt % graphite is depicted in the SEM micrographs depicted inFIGS. 7-10.

The invention of this application has been described above bothgenerically and with regard to specific embodiments. Although theinvention has been set forth in what is believed to be the preferredembodiments, a wide variety of alternatives known to those of skill inthe art can be selected within the generic disclosure. The invention isnot otherwise limited, except for the recitation of the claims set forthbelow.

1. A composition for forming a closed cell, rigid thermoplastic polymerfoam having a water vapor permeability ranging from 1 to 1.5 peen inch,the composition comprising: a foamable polymer material; at least oneblowing agent; and an additive blend including polyethylene oxide havingthe formula

where n=5-50 and R and R′ are independently H, CH₃, C₂H₅, C₃H₇, or otherhomologs and a styrene maleic anhydride copolymer having the formula

where m=100-2500 and n=100-2500; wherein the additive blend is presentin an amount from 0.5 to 3% by weight of the composition.
 2. Thecomposition of claim 1, wherein said polyethylene oxide is anethoxylated polyethylene oxide having the formula

where n=5-50.
 3. The composition of claim 1, further comprising at leastone infrared attenuating agent.
 4. The composition of claim 3, whereinsaid one or more infrared attenuating agent is selected fromnanographite, carbon black, powdered amorphous carbon, activated carbon,asphalt, granulated asphalt, milled glass, fiber glass strands, mica,black iron oxide, metal flakes, metal oxides, carbon nanotube,nanographene platelets, carbon nanofiber, activated carbon, titaniumdioxide and combinations thereof.
 5. The composition of claim 3,wherein: said foamable polymer material is present in said compositionin an amount from about 60% to about 95% by weight of the total drycomponents of the composition; said at least one blowing agent ispresent in said composition in an amount from about 4.0% to about 10.0%by weight of the total dry components of the composition; said additiveblend is present in said composition in an amount from about 0.5% toabout 5.0% by weight of the total dry components of the composition; andsaid infrared attenuating agent is present in said composition in anamount from about 0.01% to about 5.0% by weight of the total drycomponents of the composition.
 6. The composition of claim 1, whereinsaid at least blowing agent is selected from hydrofluorocarbons, C₁ toC₉ aliphatic hydrocarbons, C₁ to C₃ aliphatic alcohols, carbon dioxide,acetone, natural gases, air, water, ketones, ethers, methyl formate,hydrogen peroxide and combinations thereof.
 7. The composition of claim1, wherein said additive blend enhances the solubility ofhydrofluorocarbon blowing agents in a polymer melt.
 8. The compositionof claim 1, wherein the closed cell, rigid thermoplastic polymer foamhas a water vapor permeability ranging from 1.1 to 1.5 perm inch, andthe additive blend comprises an amount from 1 to 3% by weight of thecomposition.
 9. A composition for forming a closed cell, rigidthermoplastic polymer foam having a water vapor permeability rangingfrom 1 to 1.5 perm inch, the composition comprising: a styrene maleicanhydride copolymer having the formula

where m=100-2500 and n=100-2500; a cell size and water permeableenhancing agent consisting of polyethylene oxide having the formula

where n=5-50 and R and R′ are independently H, CH₃, C₂H₅, C₃H₇, or otherhomologs; and at least one blowing agent; wherein the styrene maleicanhydride copolymer and the cell size and water permeable enhancingagent is present in an amount from 0.5 to 3% by weight of thecomposition.
 10. The composition of claim 9, wherein said polyethyleneoxide is an ethoxylated polyethylene oxide having the formula

where n=5-50.
 11. The composition of claim 10, wherein said one or moreinfrared attenuating agent is selected from nanographite, carbon black,powdered amorphous carbon, activated carbon, asphalt, granulatedasphalt, milled glass, fiber glass strands, mica, black iron oxide,metal flakes, metal oxides, carbon nanotube, nanographene platelets,carbon nanofiber, activated carbon, titanium dioxide and combinationsthereof.
 12. The composition of claim 9, further comprising at least oneinfrared attenuating agent.
 13. The composition of claim 9, wherein saidat least blowing agent is selected from hydrofluorocarbons, C₁ to C₉aliphatic hydrocarbons, C₁ to C₃ aliphatic alcohols, carbon dioxide,acetone, natural gases, air, water, ketones, ethers, methyl formate,hydrogen peroxide and combinations thereof.
 14. The composition of claim9, wherein said composition is free of added polystyrene.
 15. Thecomposition of claim 9, wherein a ration of styrene to maleic anhydridein said styrene/maleic anhydride copolymer (S:MA) ratio ranges from70:30 (S:MA) to 99:1 (S:MA).
 16. The composition of claim 9, wherein therigid thermoplastic polymer foam has a water vapor permeability rangingfrom 1.1 to 1.5 perm inch, and wherein the styrene maleic anhydridecopolymer and the cell size and water permeable enhancing agentcomprises an amount from 1 to 3% by weight of the composition.
 17. Arigid, closed cell thermoplastic polymer foam product comprising: anextruded foamable composition having a water vapor permeability rangingfrom 1 to 1.5 perm inch, said foamable composition including: a foamablepolymer material; at least one blowing agent; and an additive blendincluding polyethylene oxide having the formula (I)

where n=5-50 and R and R′ are independently H, CH₃, C₂H₅, C₃H₇, or otherhomologs and a styrene maleic anhydride copolymer having the formula(II)

where m=100-2500 and n=100-2500; wherein the additive blend is presentin an amount from 0.5 to 3% by weight of the extruded foamablecomposition.
 18. The thermoplastic polymer foam product of claim 17,wherein said polyethylene oxide is an ethoxylated polyethylene oxidehaving the formula (III)

where n=5-50.
 19. The thermoplastic polymer foam product of claim 17,wherein said at least blowing agent is selected from hydrofluorocarbons,C₁ to C₉ aliphatic hydrocarbons, C₁ to C₃ aliphatic alcohols, carbondioxide, acetone, natural gases, air, water, ketones, ethers, methylformate, hydrogen peroxide and combinations thereof.
 20. Thethermoplastic polymer foam product of claim 17, further comprising aninfrared attenuating agent selected from nanographite, carbon black,activated carbon, powdered amorphous carbon, asphalt, granulatedasphalt, milled glass, fiber glass strands, mica, black iron oxide,metal flakes, metal oxides, carbon nanotube, nanographene platelets,carbon nanofiber, activated carbon, titanium dioxide and combinationsthereof.
 21. The thermoplastic polymer foam product of claim 20, whereinsaid additive blend increases the average cell size of said foam productincluding said infrared attenuating agent compared to foam productsformed without said additive blend and including said infraredattenuating agent.
 22. The thermoplastic polymer foam product of claim17, wherein said additive blend increases the water vapor permeabilityof said foamed product without detrimentally affecting the physical orthermal properties of said foamed product.
 23. The thermoplastic polymerfoam product of claim 22, wherein said additive blend enhances thesolubility of hydrofluorocarbon blowing agents in a polymer melt. 24.The thermoplastic polymer foam product of claim 17, wherein saidadditive blend provides a cell size from about 0.1 mm to about 0.2 mm insaid polymer foam product.
 25. The thermoplastic polymer foam product ofclaim 17, wherein the extruded foamable composition has a water vaporpermeability of ranging from 1.1 to 1.5 perm inch, and the additiveblend comprises an amount from 1 to 3% by weight of the extrudedfoamable composition.
 26. A method of forming a rigid, closed cell foamproduct comprising: heating at least one alkenyl aromatic polymermaterial and an additive blend including polyethylene oxide having theformula

where n=5-50 and R and R′ are independently H, CH₃, C₂H₅, C₃H₇, or otherhomologs and a styrene maleic anhydride copolymer having the formula

where m=100-2500 and n=100-2500 to a first temperature sufficient tomelt said at least one polymer material and foam a polymer melt;incorporating one or more blowing agents into said polymer melt at afirst pressure to faun a foamable gel; cooling said foamable gel to asecond temperature, said second temperature being less than said firsttemperature; and extruding said cooled polymer melt at a pressuresufficient to form a rigid, closed cell extruded foam product having awater vapor permeability ranging from 1 to 1.5 perm inch; wherein theadditive blend is present in an amount from 0.5 to 3% by weight of therigid, closed cell extruded foam product.
 27. The method of claim 26,wherein said polyethylene oxide is an ethoxylated polyethylene oxidehaving the formula

where n=5-50.
 28. The method of claim 26, wherein said at least blowingagent is selected from hydrofluorocarbons, C₁ to C₉ aliphatichydrocarbons, C₁ to C₃ aliphatic alcohols, carbon dioxide, acetone,natural gases, air, water, ketones, ethers, methyl formate, hydrogenperoxide and combinations thereof.
 29. The method of claim 26, whereinsaid heating step further comprises heating an infrared attenuatingagent to incorporate said infrared attenuating agent into said polymermelt.
 30. The method of claim 26, wherein said additive blend and saidat least one processing aid are simultaneously or substantiallysimultaneously added to said polymer melt.
 31. The method of claim 26,further comprising: compounding said additive blend in a carrier;pelletizing said compounded additive blend to form a pellet; and addingsaid pellet to said polymer melt.
 32. The method of claim 26, whereinthe additive blend comprises an amount from 1 to 3% by weight of therigid, closed cell extruded foam product.